This invention pertains to electronic switches and, more particularly, to a Gallium Arsenide (GaAs) field effect transistor switch suitable for switching radio frequency signals.
GaAs transistors have been used in electronic switches and are sometimes preferred over PIN diodes because these transistors can be integrated on a monolithic integrated circuit chip and because they dissipate negligible power in the ON state. GaAs transistors are usually preferred over other field effect transistors because of their high frequency operating characteristics.
GaAs transistors, however, have several disadvantages. First, GaAs field effect transistors are depletion mode devices which require a negative bias voltage (for an N-channel device) between the gate and source terminals to switch the transistor to the OFF state. This requires an additional power supply to operate the switch. Second, currently available GaAs transistors have a drain to source breakdown voltage of approximately 18 Volts. Exceeding this breakdown voltage causes irreversible damage. Consequently, GaAs transistors can only be used to switch signals up to approximately three (3) Watts, assuming a fifty (50) Ohm load.
The GaAs switch described below, however, not only permits the switching of higher power signals, but also eliminates the need for an additinal bias voltage supply by deriving the necessary bias voltage directly from the input signal to the switch.